As for a color metallic pigment having an excellent design performance and a metallic feeling, a color metallic pigment produced by adhering a color pigment onto a metallic pigment is known heretofore. In the color metallic pigment, an organic pigment of a diketopyrrolopyrrole type, a quinacridon type, a dioxazine type, an isoindolinone type, a condensed azo type, a thren type, a perinone type, a perylene type, a phthalone type, a phthalocyanine type or the like, or an inorganic pigment such as iron oxide or carbon black is used as the color pigment to be adhered onto the metallic pigment.
However, the color metallic pigment as mentioned above has such a disadvantage that a color pigment adhered onto the surface of a metallic pigment is easily optically deteriorated by the reflection of light on the surface of the metallic pigment. For overcoming this disadvantage, it is necessary to select a pigment having relatively superior light resistance, such as phthalocyanine green, phthalocyanine blue and iron oxide, and therefore it is the today's situation that the design performance of the resultant color metallic pigment is restricted.
Meanwhile, with respect to a pearlescent pigment such as mica, a pigment produced by forming a covering film of silicon oxide, titanium oxide, a metal or the like on the surface of a pigment to impart an interference color to the pigment is known. However, the pearlescent pigment has such a disadvantage that the obliterating power is poor and, therefore the pearlescent pigment cannot obliterate an under layer satisfactorily when the pearlescent pigment is compounded to a coating material or an ink. For the purpose of avoiding this disadvantage, a metallic pigment that is colored by covering with an interference film made of silicon oxide, aluminum oxide, titanium oxide or the like has been disclosed as a metallic pigment having high obliterating power. This metallic pigment is, however, insufficient as a means for overcoming the disadvantage.
Japanese Patent Laying-Open No. 01-110568 (PTL 1) and Japanese Patent Laying-Open No. 02-000669 (PTL 2) disclose methods for allowing titanium oxide to be deposited on the surface of a metallic pigment by a sol-gel method. However, the methods have such disadvantages that it is impossible to obtain a metallic pigment having high chroma, and that the titanium oxide layer is converted into a highly active anatase phase and therefore the deterioration of a resin is accelerated when compounded to a coating material or the like, often leading to the deterioration in weather resistance.
Japanese Patent Laying-Open No. 56-120771 (PTL 3), Japanese Patent Laying-Open No. 01-311176 (PTL 4), and Japanese Patent Laying-Open No. 06-032994 (PTL 5) disclose methods for forming a composite layer made of a metal oxide such as iron oxide or titanium oxide and carbon, a metal, a metal oxide or the like on the surface of a metallic pigment by a gas phase method. However, when a gas phase method is employed, it is required to fluidize the metallic pigment, supply a precursor of the metal oxide, and allow the metal oxide to be deposited on the surface of the metallic pigment by heating. Further, this deposition method has such disadvantages that it is required to use a specialized apparatus, that there is a high risk of explosion of dusts of the metallic pigment, and that most of precursors of metal oxides are highly toxic and therefore are difficult to handle.
Japanese Patent Laying-Open No. 08-209024 (PTL 6) discloses a multi-layer covered metallic pigment basically having a dual layer structure including a colorless covering layer having a refractive index of less than or equal to 1.8 and a selectively absorbing layer having a refractive index of greater than or equal to 2.0. In PTL 6, a method is disclosed in which a metal oxide layer is formed on the surface of a metallic pigment by a CVD method (chemical vapor deposition method) or a method of hydrolyzing a metal compound in a solution. However, the CVD method, which is a gas phase method, has the above-mentioned disadvantage. Further, the method of hydrolyzing a metal compound in a solution to form a metal oxide layer has such a disadvantage that the hydrolysis reaction is carried out in a basic or acidic atmosphere containing a large amount of water and therefore a reaction between the metallic pigment and water occurs during the treatment step, leading to the aggregation of the metallic pigment or the runaway of the reaction.
Japanese Patent Laying-Open No. 07-258579 (PTL 7) discloses a luster pigment produced by coating a multi-layer film that includes a first layer containing silicon oxide, silicon oxide hydrate, aluminum oxide or aluminum oxide hydrate, a second layer containing a metal and/or a non-selectively absorbing metal oxide, and optionally a third layer containing a colorless or selectively absorbing metal oxide onto a backing layer made of an aluminum flake or the like.
However, in the method disclosed in PTL 7, the thickness of the first layer tends to be non-uniform and therefore good chroma cannot be achieved. Further, there is also a problem that the metal oxide tends to be released without being deposited on the surface of the backing layer during the formation of the first layer, reflected light is scattered by the released metal oxide particles, and therefore good metallic gloss cannot be achieved. Furthermore, as the method for forming the metal oxide layer on the first layer, a CVD method and an electroless plating method are disclosed. However, in the CVD method, there is a problem as mentioned above, and there is also a problem that it is difficult to deposit the metal oxide layer uniformly and particles on which the metal is not adhered may be often produced. When the electroless plating method is employed, there is also a problem that it is difficult to deposit the metal oxide layer finely and uniformly and the metal oxide layer is deposited non-uniformly in a scattered form, resulting in the development of undesirable chroma.
Japanese Patent Laying-Open No. 2003-049093 (PTL 8) discloses a multi-layer lucent pigment containing a metal base material and multiple layers each surrounding the base material completely, which is characterized by containing at least one layer pack that includes a colorless dielectric layer made of a material having a refractive index of less than or equal to 1.8 and a colorless dielectric layer made of a material having a refractive index of more than 1.8, and a selectively or non-selectively absorbing layer. Japanese Patent Laying-Open No. 2003-131029 (PTL 9) discloses an optical multi-layer system containing a metal base material and multiple layers applied onto both surfaces or one surface of the metal base material, which is characterized by having at least one layer pack that includes a colorless dielectric layer made of a material having a refractive index of less than or equal to 1.8 and a colorless dielectric layer made of a material having a refractive index of more than 1.8, and a selectively or non-selectively absorbing layer, wherein both of the layer pack and the selectively or non-selectively absorbing layer do not surround the metal oxide layer completely. Japanese Patent Laying-Open No. 2003-089758 (PTL 10) discloses a high-chroma scale-like pigment produced by covering the entire surface of a metal-oxide-covered scale-like base that is covered with a metal oxide to develop an interference color with a translucent metal thin film capable of enhancing the interference color. Japanese Patent Laying-Open No. 2003-041150 (PTL 11) discloses a highly corrosion-resistant scale-like metallic pigment characterized by having a covering layer, which contains a hydrated metal oxide made of a metal selected from the group consisting of silicon, aluminum, zirconium, titanium and tin, on the surface of a scale-like metal base that is treated with a phosphoric acid compound and/or a boric acid compound. However, in the methods disclosed in PTLs 8 to 11, there is a limitation on the degree of change in an interference color or the development of high chroma and, therefore, it is difficult to obtain a color metallic pigment having a satisfactory level of good design performance.
A color metallic pigment disclosed in International Patent Publication No. 2007/094253 pamphlet (PTL 12) has a structure containing a metallic pigment, an amorphous silicon oxide film layer formed on the surface of the metallic pigment, a metal layer formed on the surface of the amorphous silicon oxide film layer, and metal particles formed on the surface of the metal layer, and this constitution enables the achievement of good design performance. However, in the color metallic pigment, there is a problem that the adhesion state of the metal particles formed on the surface thereof is instable and, therefore, the color tone tends to be changed easily. There is also a problem that the metal layer that exists as an unavoidable component between the metal particles and the amorphous silicon oxide film layer is not registered as a cosmetic raw material and, therefore, the use of the metal layer for cosmetic purposes is restricted.